Commit Message

This is a note to let you know that I have just added a patch titled
btrfs: use rcu_barrier() to wait for bdev puts at unmount
to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Luis
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From fb5e30677089e58d058977d56fc63afcd3a1d32b Mon Sep 17 00:00:00 2001
From: Eric Sandeen <sandeen@redhat.com>
Date: Sat, 9 Mar 2013 15:18:39 +0000
Subject: [PATCH] btrfs: use rcu_barrier() to wait for bdev puts at unmount
commit bc178622d40d87e75abc131007342429c9b03351 upstream.
Doing this would reliably fail with -EBUSY for me:
# mount /dev/sdb2 /mnt/scratch; umount /mnt/scratch; mkfs.btrfs -f /dev/sdb2
...
unable to open /dev/sdb2: Device or resource busy
because mkfs.btrfs tries to open the device O_EXCL, and somebody still has it.
Using systemtap to track bdev gets & puts shows a kworker thread doing a
blkdev put after mkfs attempts a get; this is left over from the unmount
path:
btrfs_close_devices
__btrfs_close_devices
call_rcu(&device->rcu, free_device);
free_device
INIT_WORK(&device->rcu_work, __free_device);
schedule_work(&device->rcu_work);
so unmount might complete before __free_device fires & does its blkdev_put.
Adding an rcu_barrier() to btrfs_close_devices() causes unmount to wait
until all blkdev_put()s are done, and the device is truly free once
unmount completes.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>Signed-off-by: Josef Bacik <jbacik@fusionio.com>Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Luis Henriques <luis.henriques@canonical.com>
---
fs/btrfs/volumes.c | 6 ++++++
1 file changed, 6 insertions(+)
--
1.8.1.2